1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor device and more particularly, to a pattern for measuring a focus of a light exposing apparatus and a method thereof that significantly decreases time requirements and enhances reliability and reproducibility.
2. Background of the Related Art
A related art light exposing apparatus for a semiconductor device manufacturing apparatus requires a process for checking whether a focus is uniform. If the focus is not within a permissible range, a focus adjusting process is performed to obtain a uniform focus. A related art method for measuring the focus involves light-exposing a semiconductor substrate having a photoresist film formed thereon using a focus measuring pattern as a mask. A photoresist film pattern formed on an upper surface of the semiconductor substrate is then compared with the focus measuring pattern.
FIG. 1 illustrates the related art focus measuring pattern, which includes a plurality of linear holes 1 each having a narrow width. Since the linear holes 1 have narrows widths, when the focus is not within the permissible range, a linear shape is not formed as the photoresist film pattern. The linear holes 1 formed at the edge portions are removed first, and a related art microscope is then used to compare the photoresist film pattern with the above-described pattern.
FIG. 2 illustrates a top view of the related art photoresist pattern obtained when a semiconductor substrate having a photoresist film pattern on its upper surface is light-exposed using the related art focus measuring pattern illustrated in FIG. 1 as a mask, while varying a focus value between a negative value (i.e., underfocus) and a positive value (i.e., overfocus). As illustrated in FIG. 2, an optimal focus is formed as an average of the underfocus and the overfocus, wherein the pattern line is removed when checking the photoresist film pattern using a related art microscope. The optimal focus based on the average value is then calibrated to a value of 0.
However, the related art focus measuring pattern and method have various problems and disadvantages. For example, the reliability of the measuring method is low because the photoresist film pattern is checked by human eyes using the microscope, and the best focus can vary when measured by different persons. Thus, the reproducibility is decreased.
Further, the positions for measuring the foci of the light exposing apparatus may vary on a wafer. Therefore, the photoresist pattern must be checked at each corresponding position by human eyes using the related art microscope, which requires about 1 hour. In addition, to check a field curvature or astigmatism, which are characteristics of the light exposing apparatus, the focus measuring operation must be performed at about 150 positions on the wafer. Therefore, measuring field curvature and astigmatism for the wafer requires about one day.
An object of the invention is to solve at least the above problems and/or disadvantages and to provide at least the advantages described hereinafter.
Accordingly, another object of the present invention is to provide a pattern for measuring a focus of a light exposing apparatus and a method thereof that significantly enhances a reproducibility and reliability of a measuring operation by automatically measuring a focus of a light exposing apparatus using an overlap measuring apparatus and thus decreases time required for measuring the focus.
Another object of the present invention is to simplify checking characteristics related to focus control of a light exposing apparatus, including measuring field curvature and astigmatism.
Another object of the present invention is to substantially reduce a time requirement for measuring a focus.
A further object of the present invention is to eliminate a zero point adjusting calibration operation, and obviate the need for microscope inspection for determining an optimal focus value.
To achieve the above objects, there is provided a focus measuring pattern for a light exposing apparatus which includes a plurality of linear patterns which are spaced-apart by a certain distance along the boundary of the holes wherein an overlap measuring pattern has a frame-shaped larger outer rectangular and a frame-shaped smaller inner rectangular.
Also, to achieve the objects of the present invention, there is provide an alternative overlap measuring pattern for forming a photoresist pattern on a substrate, comprising an outer frame, an inner frame positioned within the outer frame wherein the inner frame and the outer frame have a rectangular shape and form a mask region that blocks the transmission of light from a light exposing apparatus, a light transmission region positioned between the inner frame and the outer frame that allows a transmission of light from the light exposing apparatus, and a focus measuring pattern positioned in the light transmission region.
Another embodiment of the present invention provides an overlap measuring pattern for forming a photoresist pattern on a substrate, comprising an outer rectangular-shaped frame having a first region and a second region, an inner rectangular-shaped frame having a third region and a fourth region, an intermediate region positioned between the outer frame and the inner frame having a fifth region and a sixth region, wherein the first region, the third region and the sixth region form a light transmission region that allows a light transmission from a light exposing apparatus, and the second region, the fourth region and the fifth region form a mask region that blocks light transmission from the light exposing apparatus, and a focus measuring pattern positioned in the light transmission region.
A further embodiment of the present invention provides an overlap measuring pattern for forming a photoresist pattern on a substrate, comprising a reference region adapted to be imaged onto a photoresist layer by a light exposing apparatus, and a focus measuring region adapted to be imaged onto the photoresist layer by the light exposing apparatus when a focus value of the light exposing apparatus falls within a predetermined range.
A focus measuring method embodying the present invention comprises the steps of forming an image that includes a reference region on a photoresist film with the light exposing apparatus, wherein the image further comprises a focus measuring region when a focus value of the light exposing apparatus falls within a predetermined range, and determining the focus value of the light exposing apparatus by measuring a distance between a first point on the reference region and either a second point on the reference region or a point on the focus measuring region.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objects and advantages of the invention may be realized and attained as particularly pointed out in the appended claims.